Synchronous motor



Sept. 14 1926. 1,599,756

V. A. FYNN smcrmouous MOTOR Filed Feb. 4. 1924 I 4 Sheets-Sheet 1#215166; @5650, Fxnw.

Sept. 14, 1926. 1,599,756

V. A. FYNN SYNCHRONOUS MOTOR Filed Feb, 4, 1924 4 Sheets-Sheet 2 ##0reg}.

Sept. 14 1926. Q r 1,599,756

I VxA. FXWQDJ' smcnnonous MOTOR Filed Feb. 4, 1924 4 Sheets-Sheet 5 fl51C].

Se t. 14 1926. 1,599,756

, v. A. FYNN smcfinouous MOTOR Filed Feb. 4, 1924 4 Sheets-Sheet 4Patented Sept. 14, 1926.

VALERIE ALFRED FYNN, or s'r. Louis, MISSOURI.

snrcimonous moron.

Application filed February 4,1924. Serial at. 690,441.

My invention relates to the starting of dynamo-electric machines inwhich a revolving field of more or less uniform magnitude is produced atleast during the starting pclied, and which derive their excitation froman exciter delivering uni-directional voltage at synchronism and slipfrequency voltage at other speeds.

It also relates to the operation of machines provided with the type ofcxciter described and more particularly, it relates to polyphasesynchronous induction motors. j

The objects and features of this invention will appear from the detaildescription taken in connection with the accompanying drawings and willbe pointed out in the claims. 7

In the accompanying diagrammaticdrawings, Figs. 1, 2, 3 and 4 showtwo-pole embodiments of my invention as applied to a separately excitedthree-phase synchronous induction motor, and Figs. 5 to 14 inclusive areexplanatory diagrams.

Referring to Fig. 1, the separately excited three-phase two-polesynchronous induction motor represented therein comprises a primarythree-phase winding 5 of any desired type located on the stationarymember or stator of the machine and connected to the three-phase supply2, 3, 4 through the adjustable ratio transformers 60, 61, 62. For thepurpose of more clearly illustrating this motor, the rotor is shown ashaving distinct .polar projections 7. The two-polerotor is provided witha two-phase winding, the elements 9 and 10 of which are displaced by 90electrical degrees and in consequence there are shown four polarprojections on the rotor, diametrically opposed projections carryingparts of the same element of the polyphase rotor winding. The element orphase 9 is connected to the slip-rings 15, 16, with which co-operatestationary brushes ,17. 18. The phase 10 is connected to the slip-rings16, 12, with which cooperate the stationary brushes 17, 13. Theslip-rings are carried by the shaft 6. The rotor further carriesanother, preferably polyaxially closed, winding shown in Fig; 1 in theform of a squirrel cage 8. Mounted on the shaft 6 of the synchronousinduction motor is an exciter} the revolving member of which carries awinding 19 adapted to be connected to the supply 2, 3, 4 by means of thesliprings 20, 21, 22 and stationary brushes cooperating with same, andalso connected to a commutator with which co-operate the brushes 24,26insulatingly held in the movable brush support 27, the position of whichcan be conveniently altered by means of the handle 28. In the figure thecommutator connected to the winding 19 is not shown, and it is assumedthat the brushes rest directly on the winding 19, thus eliminating alluncertainty as to their position relatively to said winding. Thestationary member co- I operating with the rotor of the exciter islaminated and carries two exciting windings 29 and 30, connected inparallel and to the brushes 24, 26 with an adjustable resistance 31, 32in the circuit of each. These windings are located on each side of theperpendicular to the brush axis, each being displaced 45 electricaldegrees from said axis. They are connected to produce a resultantmagnetization which can be shifted through 90 degrees by manipulatingthe resistances 31, 32 and through an additional 90 by reversing one ofthem. 26 are connected to the slip-rings 15, 16 with the interpositionof the adjustable resistance 34. Brush 24 is also connected to slip-ring12 with the interposition of the adjust-ablev resistance 33. Theslip-rings 15, 16 are shunted by means of the adjustable resistance 35and the slip-rings 16, 12 by means of the adjustable resistance 36. TheWinding 19 on the revolvingmember of theexciter is connected to themains 2, 3, 4 with the interposition of a phase regulator, the primary37 of which is stationary and connected to the supply 2, 3, 4 while itssecondary 38 can be rotated within the primary by means of the handle39, thus causing the phase of the polyphase E. M. F.s impressed on theslip-rings 20, 21, 22 to assume any desired relation with respect to thephase of the line E. M. F.s. The primaries of the series transformers43, 44, 45 are included in the connections between the primary Thebrushes 24 and I winding 5 of the synchronous induction motor and thesupply 2, 3, 4. Similarly, the secondaries of the series transformers40;

41, 42. are included in the connections between the primary 37 of thephase regulator the series transformers 43, 44, 45 are conand'the supply2, 3, 4. The secondaries of of brushes 23, are displaced from the brushset 2d, 26 by 90 electrical degrees. The exciter brushes 2 1, 26 areconnected to the slip-rings 15, 16 through the adjustable resistance andthe QD-ICliQl' brushes 23, 2: to the Silk ngs 11, 1 through the adjust-The two slip-ring windings can be connected in parallel with respect toeither set of exciter brushes by means of the switch and the adjustableresistance 81-. The stator of the exciter carries two exciting windings29 and 30, the first being connected to the brushes 2-1, 26 with theinter-position of theadjustable resistance 31 and the second to thebrushes 2:5, 25 through the adjustable resistance 32.

In Fig. 3 the three-phase star connected primary winding 5, 5", 5 islocated on the rotor and connected to the supply 2, 3, 4 throughslip-rings and brushes co-operating with same. The stator carries athreephase star connected winding 19, 19", 49 and a squirrel cage 8.Mounted on the shaft 6 of the motor is the armature of the conyerterexciter with a three-phase winding 19 connected to a commutator and tothree points 46, e7, 18 of the primary 5 of the motor. The said pointsare so chosen with reference to the zero point of the star winding 5 asto produce exciter brush voltages of the desired magnitude and the threepoints 67, 68, 69 of the winding 19 are so selected as to give saidvoltages the desired phase for a selected position of the brushes 54,55, 56. The stator of this exciter carries two exciting windings 29 and30, displaced by electrical degrees, and a movable brush support 27provided with a handle 28. The brush support insulatingly carries thebrushes 54, 55, 56.displaced by 120 electrical degrees and co-operatingwith the commutator connected to 19. The windings 29 and 30 areconnected in parallel and to the brushes 54, 55 with an adjustableresistance 81, 32 in the circuit of each. These windin s are located oneach side of the perpen icular to'thebrush axis, each being displaced 45electrical degrees from said axis. They are connected to produce aresultant magnetization which can be shifted through 90 degrees by maniulating the resistances 31, 32 and througii an additional 90 byreversing one of them. The secondary stator winding 49, 49", 49', can beshunted or short-circuited by the adjustable three leg resistance 50 andone of the adjustable' resistances 51, 52, 53 is included between anexciter brush and a terminal of the secondary motor winding 49.

Fig. 4: also shows a two-pole three-phase induction motor. The stator isthe primary and carries a three-phase winding5 connect- 'ed to thesupply 2, 3, 4, the rotor is the secondary and carries a permanentlyshort-circuited four-phase winding 8 and a star connected three-phasewinding 19 joined to the slip-rings 11, 12, 15 mounted on the shaft 6and with which co-o erate the stationary brushes 11, 13, 18. hounted onthe same shaft 6 is the member 7 1 of the exciter provided with theexciting winding 57 and insulatiugly carrying the brushes 54, 55, 56 bymeans of the brush support 27 which revolves with 74. The stationarymember of the exciter carries a three-phase winding 19 provided with acommutator with which cooperate the brushes 5 1, 55, 56 and connected tothe supply 2, 3, 1 through the adjustable three-phase transformer 78.The points of connection of the supply to 19 can be varied by means ofthe switches 70, T1, T2 and the taps 73 on the winding 19. The brushesare connected to the slip-rings 75, 76, T7 mounted on the shaft 6. Theregulating devices for the circuits comprising the winding 4.9 areincluded between the slip-rings to which the exciter brushes areconnected and those to which the three terminals of 19 are joined. /Vhenregulation of said circuits is not desired all the slip-rings can beomitted. The adjustable resistance 51 is included between the slip-ringsT5 and 11, the adjustable resistances 52 and 53 between the sliprings76, 12 and 77, 15. The three leg resistance 50 is connected to theslip-rings ll, 12, 15 to shunt and short-circuit the threephase winding49.

The motors shown in Figs. 1, 2, 3 and 4 can be started, synchronized andoperated in different ways according to the results it is desired tosecure. Referring more particularly to Fig. 1, let it first be assumedthat the secondary winding 10 on the rotor of the motor, the slip-ring12 and the resistance 33 are omitted. The motor can be started in somewell known way as an induction motor, particularly if the rotor is builtwithout polar projcctlons and carries a polyphase winding located anddistributed as is usual in induction motors.- The squirrel cage 8 can doduty as a secondary, and the transformers 60, 61, 62 can be used tolower the terminal voltage at starting. During the early stages thecircuit of the rotor winding 9 can either be open or closed over asuitably high resistance 34 and the brushes 24, 26 of the exciter,thereby protecting the commutator of the exciter from the heavy startingcurrents. Under these conditions the motor will run up to a nearlysynchro uency and could not synchronize with anyt ing like full loadtorque with anywhere near normalexcitingcurrent and particularly not ifit had been designed for'good induction motor starting characteristicandhigh weight efficiency, which is, of course, very desirable. Ifalternating current of slip frequency but of a phase difierin materiallfrom that here defined is fe into the winding 9 and an attempt is madeto regulate the phase of the current in 9 due to this alternatingvoltage in order to improve the synchronizing torque, the result willalso be unsatisfactory because the slip fre uency is so small as topreclude the pos sibi ity of materially influencing the phase of thiscurrent. The resultant synchronizing torque will be of double the slipfrequency. According to this invention I connect the winding 9 to anexciter 19 which, at speeds differing from the synchronous, suppliesalternating voltage of slip frequenc and of such phase that theresulting sync ronizing torque is unidirectional, or substantially so,and preferably only pulsates and does not reverse. Just how the base ofthis voltage of slip frequency is to e selected and how thissynchronizing tor ue is produced will be stated hereafter. his voltagecan be applied at any time during the starting period; in the largermotors it will preferably be applied in the latter part of said period.

The phase of this voltage which is derived.

from the brushes 24, 26 can be adjusted in F i 1 either by adjusting thephase of the voltages impressed on the slip-rings 20, 21, 22 of theexciter by means of the phase regulator 37, 38, or y displacing theexciter brushes on the commutator by means of the brush carrier 27 andits handle 28. \Vhen a phase regulator is provided it is obviouslysimplest to use it for making said adjustment. It is not necessary touse a phase regulator and adjustable brushes, one of these adjustingmeans can be dispensed with. Nor is it necessary when using a phaseregulator to have the secondary 38 thereof movable. It is obviously euivalent to move the points at which the lea s from the slip-rings 20,21, 22 are connected to the secondary 38.

Except for experimental urposes orin cases where the starting load 0aracteristic of the motor is to be widely varied in use, the'lattermethod is clearly preferable since it is not usually necessary to alterthe adjustment after it has once been correctly made. In all cases thephase. regulator can do duty as a. reducing transformer as well as aphase adjuster.

The exciter 19, being supplied with line frequency currents over itsslip-rings 20, 21, 22, a revolving flux is produced by 19 and theconnections are such that said flux is caused to revolve oppositely tothe direction of rotation of 19 which is determined by that of the rotor7 of the motor. The frequency of the brush voltage will then always beproportional to the slip of the motor becoming zero at synchronism, atwhich speed the exciter supplies a. unidirectional voltage.

Assuming now that the base of the brush voltage, so long as it is aternating, has been chosen in accordance with this invention, the motorwill develop a powerful and most effective synchronizing torque evenwhen the resistance 34 is so set during the synchronizing period as toproduce, without change in setting, the desired unidirectionalexcitation of the motor at synchronous speed. The ma chine will pullinto step with considerable overload and continue to operate as asynchronous motor.

This substantially unidirectional torque will effectively and smoothly,bridge the gap between the decreasing induction motor torque whichbecomes zero at synchronisin and the synchronous motor torque, afterwhich the machine will operate as a synchronous motor. If loaded beyondits torque capacity as a synchronous motor, the machine will slipbaclcinto asynchronous op eration, the gap between the synchronous andasynchronous torqueagain being bridged by the synchronizing torque.

While operatin as" a synchronous motor it will exhibit theself-regulating or compounding characteristic inherent to allsynchronous motors excited from a converter, whether the latter isintegral with the motor as in some self-excited synchronous motors, forinstance in that disclosed in U. S. P. 1,337,648, or is independent fromthe motor as in Fig. 1, in U. S. P. 1,331,055 and in other knownseparately excited synchronous motors. This self-regulation affects theexcitation of the motor and is brought about by the fact that theperiodical space relation of the two members of asynchronous motorchanges with load. In this case the rotor 7 will momentarily check oraccelerate its angular velocity in response to a change in load, orexcitation, and thus change its periodical space relation with referenceto the stator 5.

But this momentary change in velocity similarly affects the periodicalspace relation between the points on winding 19 to which the slip-rings20, 21, 22 are connected, and

which move with 7, and the brushes 24, 26; This change brings about achange in the magnitude of the exciting voltage which accounts for theinherent and automatic selfregulatin'g feature of this class of machine.

How to properly take advantage of this feature in operating this machinewill be ex- The inherent regulation just referred to may not besufiicient for all purposes or it may be desirable to secure a somewhatdifferent variation of th exciting voltage. This can be done, forinstance, by means of the series transformers 43. 44, 45 and 40, 41, 42.

These may be so connected that as the currents taken by the motorincrease, the voltages impressed on the slip-rings 20, 21, 22 of theeaciter are either lowered or raised, their phase being also affectedaccording to the relation of the phases of the motor currents to thephasesof the supply voltages. These series transformers need not alwaysbe used.

The exciting windings 29, 30 located on the stationary member of theexciter can be omitted. Their main purpose is to control the powerfactor of the exciter at its sliprings or of the exciter slip-ringcircuits at the points or" their connection to the supply 2, 3, 4.Because the moving member of this converter-enciter is mechanicallycoupled to the revolving member of the motor it is not free to adjustitself to changes of exciter load or excitation and a more uniform powerfac- 'tor can often be obtained by locating the axis oi: the resultantunidirectional exciter excitation an angle to the axis of the brushesconnected to the winding or windings pro- .dncing said excitation. Ifthe position of the brushes is changed for one reason or another thedesired relation between theaxis of the resultant magnetization due to29 and 30 and the brush axis can be at once re-established bymanipulating the resistances 31, 32 or reversing one oi the windings 29or 30 as heretofore explained.

When the winding 10 and the slip-ring l2 of Fig. i are available, themachine may be sta' exactly as just described except that the slip-ringwindings 9 and IQ are connected parallel and to the brushes 24,26through the resistances 34 and 33. It will be seen t at the so connectedwindings will produce resultant magnetization F dependent on themagnitude and direction of thecomponent magnetization h and is producedby 9 and 16 respectively; When the components are oi equal magnitude anddisplaced by 90 degrees, the resultant will be displaced by 45 degreesmmeach com nent as shown by the small diagram in F1 1; The phase of thealternating brush v tage is in this case chosen with reference to theaxis of this resultant rotor magnetization, otherwise the procedure isexactly as previously described.

When two phase displaced slip-ring windings such as 9 and are availablethe compounding characteristic of the machine can e very readily changedby changing the relation of the unidirectional ampere turns in 9 and in10.

The motor of Fig. 1 can also be started with or without the use of thesquirrel cage 8 by interruptin the connection between the commutator anthe windings 9 and 10 or giving the resistances 33 and 34 a suflicientlyigh value to protect the commutator and then close said windings overthe resistances 35 and 36, starting the machine just like a slip-ringinduction motor. When up to speed 35 and 36 are disconnected in one ormore steps and 33 and 34 reduced in one or more steps to their operatinvalues. The machine will synchronize as diefore and its compoundingcharacteristic may be modified by one of the means available for thispur pose. If a squirrel cage 8 or its equivalent is used, it ispreferably given a high resistance and allowed to take care of theinitial starting torque.

Turning now to Fig. 2. The machine may be started as an induction motorwith the help of a winding such as 8, which is or can be closed along aplurality of axes per pole pair or it can be started like a slip-ringmotor by reducing the resistances 35 and 36 to zero in one or moresteps. These two methods can, of course, be combined. After the machinehas reached what is considered to be a sufliciently high speed and ifthe resistances 35, 36 are being used, they are disconnected in one ormore steps and the resistances 33, 34 reduced in one or more steps totheir synchronizing value. Assuming that the phase of the polyphasealternating brush voltages has been chosen in accordance with thisinvention, a practically uniform synchronizing torque will be developedwhich will readily bring the motor into step even with the heaviestoverload the machine can handle. When synchronous speed has beenreached, all but one of the brush circuits are disconnected or theirresistance greatly increased. In Fig. 2 I prefer to disconnect, say, thebrushes 23, 25 at 33 and connect 10 in parallel to 9 and the brushes 24,26 by closing switches 80 and 81 and adjusting the resistance of thecircuits comprising 9 and 10 to secure the desired operatingcharacteristic.

When a polyphase arran ement of exciter brushes and a correspon ingpolyphase arrangement of secondary motor windings are available and themotor is not lar e or the starting torque to be developed in a argemotor is not great, then such resistances as 35, 36 may be dispensedwith and the machine started and synchronized by closing the motorsecondaries over the exciter brushes and reducing the resistances 33, 34

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brush circuits connectedto the secondary of,

the motor, one of the exciter brush voltages is likely to be higher thanthe other, in fact, one may be substantially at its maximum while theother is substantially zero. The

' least disturbance is created when the latter circuit is disconnectedand generally speaking, when the lower exciter voltage circuit isdisconnected independently of Whether the speed is synchronous or not.It is not necessary to make use of two exciting windings 29 and 30 011the exciter. If one only is used, then it is best to disconnect aftersynchronizing those exciter brushes which are not connected to anexciter exciting winding.

Turmng now to Fig. 3, this can be operated in substantially the same wayas Figs. 1 or 2, notwithstanding the fact that the motor primary is onthe rotor and its secondary on the stator. I The winding 49 is connectedto the brushes 54,55, 56 of the exciter without the interposition ofslip-rings because the windingandthe brushes are stationary. Because 49is a three-phase winding, the polyphase arrangement of brushes on thecommutator of the exciter is also threephase. The motor can be operatedwith or without the permanently short-circuited winding 8. If 8 is notused or has a high resistance, then the three leg resistance 50 ispreferably used at starting just like in an ordinary induction motor.Assuming that the phase adjustment for synchronizing the motor is somade that a substantially uniform pulsating synchronizing torque isdeveloped by 49 when connected to the brushes 54, by 49v when connectedto the brushes 55, 56 and by 49 when connected to the brushes 56, 54,then such a torque can be produced with the resistance 50 in use, forinstance by disconnecting 49' from 50 in one or more steps andconnecting brush 54 to 49 through 51 and brush 55 to 49" through 52 andadjusting the values of 51 and 52 in one or more steps to theirsynchronizing or operating values. A pulsating synchronizing torque canbe similarly produced with any other pair of exciter brushes. If apulsating synchronizing torque is suflicient for the use in view, thenthe exciter brush 56 and the resistance 53 can be omitted. Aftersynchronizing, the connections just described need not be disturbed butvthe resistance in the exciter brush circuit can be adjusted to anydesired value. To secure a substantially constant synchronizing torquethe phases 49, 49", 49" are disconnected from the resistance 50 in oneor more steps and the brushes 54, 55, 56 preferably simultaneously.-

connected to the corresponding phases by'] reducing the adjustableresistances 51, 52, 53 in one or more steps to their synchronizingvalues. Thereafter, and if desired, two of the phases may beshortcircuited in series by means of 50 and the combination thus formedleft connected to the brushes which j produce a pulsating synchronizingtorquewith the third phase. Thus, 49" and 49" can be short-circuitedover 50 and the brush 56 disconnected at 53. If the machine issynchronized with a polyphase torque and the connections between exciterand secondary of the motor are thereafter changed, it is here,,as in allother cases, preferable to let those brushes provide the unidirectionalexcitation at synchronous speed which are connected to the excitingwinding or windings on the secondary of the exciter. The desiredrelation between the axis of the resultant magnetization produced by thesecondary of the exciter and any exciter brush axis is brought about bysuitably manipulating the resistances 31 and 32.

Here the phase and the magnitude of the voltages impressed on 19 are notreadily accessible for adjustment after completion of the machinebecause derived from part of the revolving primary of the motdr. In sucha case the connections between 5 and 19 will be made as correctly aspossible when building the machine and final adjustments, if needed,carried out by displacing the brushes. In all cases it may be convenientto make the final adjustments by brush displacement.

Fig. 4 differs from Fig. 1 in that the secondary of the motor-carries athree-phase instead of a two-phase winding with a corresponding changein the polyphase arrangement of brushes on the exciter and in that theprimary of the converter-exciter is located on the stator instead of onthe rotor of the exciter. This change makes no difference to themannerof operation and this modification can be operated just like the otherhere described. Since the brushes of the exciter revolve they areinaccessible for adjustment during operation. These brushes, togetherwith the member 7, can be keyed on the shaft 6 in as nearly correctposition as is possible in order to produce a substantially pulsating ora substantially constant synchronizing torque when the supply isconnected to certain points of the stationary winding 19 through theadjustable ratio transformer 78 and further adjustments, if needed, canbe made by shiftmg these points of connection by means of the switches70, 71, 72 and the taps 73 attached tothe winding 19.

According to this invention, one or more voltages derived from anindependent exciter are applied to one or more secondary ages in thewindings to which they are apchronously and clockwise in space.

plied, they must be unidirectional at synchronous speed and of slipfrequency at other speeds. At synchronism this voltage or voltages willproduce a unidirectional magnetization; for the sake of convenience,

1 they will be referred to as synchronizing voltages.

In order to show how the phase of a synchronizing voltage is to beselected or adjusted and how the synchronizing torque is produced, it isnecessary to go to some extent into the theory of operation of theseparately excited synchronous motor here described. In Fig. 5 is shownthe revolving secondary member Y of the motor of Fig. 1 and therevolving primary 19 of the exciter, both keyed to the same shaft 6 andtherefore both revolving in the same direction. The secondary member 7has four polar projections or four large slots and is laminatedthroughout. The polar projections are spaced by half a pole pitch and Pin Fig. 5 measures the pole pitch of this two-pole motor. The brushesco-operating with the exciter winding 19 are located at random. If theprimary 5 of the motor produces a revolving flux F, which revolves in aclockwise direction, then the rotor 7 starting as the secondary of aninduction motor will revolve in the same direction and will cause theexciter 19 to also revolve clockwise. But the exciter 19 is to provide aunidirectional enciting voltage at synchronism, and for this reason thewinding 19 must, through its slip-rings 20, 21, 22 be connected to theline 2, 8, 4 in such a way that with 19 at rest the revolving fluxproduced by 19 will revolve counterclockwise. Under these conditions,this flux f will become stationary in space when the exciter revolvessynchronously in a clockwise direction. After the machine has reached ashigh a speed as the induction motor torque can produce, the conditionsare as follows: F revolves syn- The rotor 7 revolves in the samedirection but at a slower rate; it slips to a certain extent. Thewinding 19 of the exciter revolves clockwise at the same speed as 7, andthe revolving iiur: f revolves counterclockwise at slip speed. Thatwhich, according to this invention, is necessary in order to produce thesingle or polyphase synchronizin torque of the nature described isfirst, that any brush voltage generated by the exciter and impressed ona secondary winding of the motor be substantially zero when the axis ofthat winding coincides with the axis of the revolving flux F set up bythe primary 5 of the motor. Second, that when the axis of said secondarywinding does not coincide with the axis of F, the direction of the brushvoltage is such that thecurrent is produced in the secondary of themotor t-f which it is applied is of a direction to produce a positivetorque in co-operation with F. In order to show the reason for theserequirements in a simple manner, let it be supposed that the secondary 7and the exciter winding 19 are standing still and that n revolves withno-load slip frequency in a clockwise and f with no-load slip frequencyin a counterclockwise direction. This is equivalent to considering theconditions obtaining at nearly synchronous speed. Not only are themeasurements which will presently be outlined more easily made when themotor and the exciter run at that speed, but the phase conditions in theprimary and secondary of the motor are not the same at starting and verynear synchronism. The phase conditions existing 'near synchronism shouldbe considered because the synchronizing torque is to be produced verynear synchronism.

Turning now to Fig. 6, let it be assumed that the member 7 carries but asingle winding 9 and has but two polar projections; also that but twobrushes 24, E26 co-operate with the commuted winding 19 of the exciter.It is further assumed that the winding 9 is located in the slots shownin Fig. 6 and placed close to the periphery of a secondary memberwithout defined olar projections such as would preferably e used inpractice. The corresponding position of a secondary member with definedpolar projections is indicated in dotted lines and this form ofsecondary member is lightly shaded to distinguish it from the rotorform. In the following Figs. 7, 8 and 9 the actual winding 9 is notshown, but the direction of the current in the rotor slots which ac--commodate this winding is indicated, the circles denoting an upwardlyand the dots or full circles denoting a downwardly directed current.With the motor running as an induction machine at nearly synchronousspeed, the revolving flux F will cutthe winding 9 at slip frequency andthe conditions will be the same as if this winding stood still and Frevolved at slip frequency. lVhen the axis of F coincides with the axisof 9 as shown in Fig. 6, then the voltage a, generated in 9 by F will bezero and near synchronism, at slip frequency, a voltmeter '0 connectedto the terminals of 9, in other words, to the slip-rings 15, 16, willdietinctly show when this voltage is zero provided the slip is smallenough. Having now selected any desired position for the brushes 24, 26,for instance having displaced them by 90 electrical degrees with respectto the resultant magnetization produced by the exciting windings 29 and30 to which they are connected, it is only necessary, in order tosatisfy the first condition laid down above,- to so manipulate or adjustthe phase relation of the polyphase E. M. F .s impressed on 19 withrespect to the polyphase E. M. F.s impressed on 5 as to cause the brushvoltage (2, measured by the volt-meter'o to become zero substantially atthe same time as 6, measured by c, is zero. Thebrush voltage 6 will bezero whenever the axis of f coincides with the brush axis. The ad- 2, 3,4 or can be made to differ from'these by any angle up to and includin180 derees. But the phase of the sync ronizing rush voltagee can also bevaried and adjusted to the desired relation by changing the points ofconnection of the supply to the winding 19 of the exciter as shown inFig.

4. Conversely, having applied to 19 voltages bearing any desired phaserelation to the supply voltages or having selected the points at which te supply voltages are connected to the winding 19 of theconverterexciter, the phase of the synchronizin voltage or voltages canbe adjusted as esired by displacing the brushes co-operating with thecommuted winding on the primary of the converter-exciter. Having soadjusted the phase of f with respect to that of F or so set the exciterbrushes as to have the voltages e, and e, pass throu h zero atsubstantially the same time an connecting avolt-meter such as o, inseries with the brushes 24, 26 and the winding 9, said voltmeter willread zero when i), and 0, read zero.

short-circuited and that F revolves with re-' spect to it at slipfrequency, then it is known that the voltage 6, generated in 9, when outby F and which voltage we have just caused to pass through zero when 6was passing through zero, is going to produce a current in 9, saidcurrent co-operating with F to produce a positive torque. In fact, thisis just the wa in'which the torque is produced in a po yphase inductionmotor, and

that the magnitude of said current and" therefore of said torque dependson the slip, diminishes as this slip diminishes and becomes zero atsynchronism' This considera-' tion clearly determines the direct onwhich the brush voltage should have. Since it is to produce a positivetorque, it will certainly do this if it is of the same phase anddirection as the voltage generated in 9 near synchronism by thesynchronous rotation of F. Under these conditions, the brush voltage,whose magnitude is independent of the slip, will continue to forcethrough the sec ondaries of the motor that current which the secondaryvoltage generated by F would have forced through that winding if it hadbeen possible to maintain said secondary voltage e as synchronism wasapproached. According to this invention, thereis intro duced into thesecondary of an induction motor a voltage or voltages of same phasedirection and periodicity as the voltage or voltages generated in saidsecondary at nearly synchronous speeds by the revolving primary flux ofthe induction motor, each of these conduced voltagesis made independentof the slip as to magnitude but dependent thereon as ,to frequency andeach converted into a unidirectional voltage as synchronism is reached.When the secondary of the induction motor has a winding such as 9 or 10in Fig. 1 with but one axis per pole. pair, then but a single brushvoltage or single-phase synchronizing voltage is used. When thesecondary of the induction motor has a winding with aplurality of axesper pole pair such as 9 and 10 in Fig. 1 or 49 in other figures, then apolyphase synchronizing voltage may be used. Injecting a single-phasesynchronizing voltage of proper phase and direction along one axis perpole pair produces a single-phase pulsating and substantiallyunidirectional synchronizing torque. Injecting polyphase Synchronizingvoltages of proper phase and direction into the secondary of the motoralong a pluralit of axes per pole pair produces a polypliasesynchronizing torque. In all cases the adjustments must be so made thatso long as the brush or synchronizing voltage is an alternating one,whether single or polyphase, "it substantially coincides as to phase anddirection with the voltage e generated by F at nearly synchronous speedsin the secondary on which itis impressed. That these deductions arecorrect can be shown by reference to Figs. 7, 8 and 9.

Having, for instance, so set the phase regulator 37, 38 as to cause thebrush voltage e to go throu h zero when the voltage e, generated in 9 yF also goes through zero, and having so connected the brushes 24, 26

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to the terminals oi 9 that in so far as 9 is concerned e is of samedirection as e,, let it further be assumed that, as in Fig. 7, the brushaxis and the axis of 9 are vertical. Starting to count time from theinstant when both fluxes F and f are in the ver tical and directeddownwardly, after each has traveled through an angle a of about l5degrees the voltage c, will be directed in 19 as shown by dot and circlewithin the circle representing 19 and will force a current through 9distributed as shown in 7 of Fig. l. The direction of e is determined bythe that f crosses the brush line 2%., 26 from left to right and thedirection of rotation of 19 is clockwise. Remembering that F isgenerated by the primary winding 5 of the motor, it will be seen that inthe position it occupies in Fi 7 it will thread the rotor 7 from ri htto left and in so doing will produce, witli the current distributionshown, a clockwise or positive torque. On the assumption of sinusoidalflux distribution and sinusoidal current and E. M. F. waves, the voltagee will at all times be proportional to sine a and that component of Fwhich is at right angles to the axis of 9, and which alone is effectivein producing torque with i), will also at all times be proportional tosine a, with the result that the torque produced will be proportional to(sine a) provided the directions here given are followed. In Fig. 8.each of the dunes F and f has traveled through 90 degrees. The brushvoltage is a maximum and all of F is effective so far as producin torquewith the ampereturns in 9 is concerned. The synchronizing tor que T is aAfter a further travel through 96 degrees, the brush voltage becomeszero and the torque is zero. As f sweeps past the vertical, the brushvoltage is reversed, as shown in Fig. 9, which depicts the conditions ofmaximum reversed brush voltage. This, of course, reverses the currentthrough 9, but F, is also reversed, with the result that torque T doesnot change its direction and r mains positive.

lhe variation as the brush voltage e, and the corresponding variationsof the torque T produced by the interaction of the synchronizingvoltage'collected 'by the brushes 2%, 26 and conductively impressed onthe secondary 9 of the synchronous induction motor are both shown inFig. 10. The time during which each positive torque impulse lasts is Iother set of brushes such as 23, are located to co-operate with 19 andare displaced by 90 electrical degrees from the brushes 24, 26, it willmake available a second single-phase brush voltage 6 in phasequadraturewith the first, and that if the directions here given withregard to 6 are applied to e, and this secondvoltage is impressed on asecond secondary such as 10 in quadrature space relation to 9, then asecond synchronizing torque, T identical in form with T,, will beproduced in phase and space quadrature with T as shown in Fig. 11. Thesum of these two torques is the constant synchronizing torque T.

Since the synchronizing torque must be developed and maintained fromthat induction motor slip which corresponds to the load to beaccelerated right up to synchronism, it is clear that during thesynchronizing period the frequency of the brush voltage or voltages willvary from about 8% of the line frequency to zero, therefore from perhapsfive cycles downwards in the case of a cycle supply. For frequencies ofthis order of magnitude, it is not possible to create any appreciablephase difierence either with a positive or a ne ative reactance and theinsertion of impe ances in the brush circuit would for this reason haveno appreciable eiiect on the result. What is needed in order to make thesynchronizing torque substantially unidirectional is to securesulliciently close phase coincidence between the brush voltage and thesecondary voltage which it is to replace. This torque will besubstantially unidirectional when negative torque impulses are reducedto a small percentage of the positive ones or entirely eliminated. Forthis same reason, phase differences between brush voltage and resultingcurrent have been neglected in connection with the discussion of Figs. 5to 9, inclusive. This discussion only applies to synchronizingconditions and these are so very near the'synchronous speed that saidphase differences are very small and can be neglected.

If a synchronizing voltage of a phase and magnitude chosen in accordancewith this invention were applied at starting to the secondary winding ofthe motor on which this voltage is impressed for synchronizing purposes.it would have practically no effeet on the starting torque or on thetorque per ampere atstartine. For one thing, its magnitude isinsullicient and its phase is unsuitable. To make it effective atstarting, its magnitude would have to be greatly increased and its phasedisplaced through about 90 degrees or even more.

For the case of a two-phase arrangement of brushes on the exciter and 9.corresponding two-phase arrangement of induced windings on the secondaryof the motor, the resultant constant polyphase synchronizing phasepulsating torque. In the ease of a three-p iase arrangement of brushesand induced windings, the resulting pol 'phase s nchronizing tor ue willhave a va ue equa to one and one ha f times the amplitude of one of thecomponent single-phase pulsating torques. f

Turnin back to the inherent regulating feature already broadlydescribed, let it be assumed that the motor of Fig. 1 has beensynchronized with a single-phase pulsating and therefore unidirectionaltorque by means of the winding 9 and the exciterbrushes 24,

. 26. Having been synchronized as stated, the

axis of the motor winding 9 must have lagged about 90 electrical degreesbehind the axis of F or the axis of a stator pole every time the voltageat the brushes 24, 26 was a maximum. See Fig. 12. Let a measure this lagin degrees. If, in synchronous operation, the axis of 9 continues torevolve in the periodical space relation of 0:90 to the axis of thestator pole it is approaching, then the now unidirectional brush voltagewill remain a maximum because the exciter recelerate and come to occupya more forward periodical space relation to the axis of a stator pole,reducing the displacement c to less than 90 electrical degrees, andcorrespondingly reducing the displacement d between the axis of f andthat of the exciter brushes 24, 26, but leaving f stationary after thistemporary movement. In this new periodical space relation and thecorrespond ingly changed position of f, the unidirectional voltage mustbe lower. It varies as the sine of d. This means that the inherentregulating property operating under the conditions determined by thesynchronizing torque setting above specified reduces the excitation withdecreasing load. Generally speaking, this is desirable but the maximumsynchronous torque is not always available for c:90 and a decrease inexciting voltage substantially proportional to sine (1 may, forinstance, be too rapid. The maximum tor ue -is more often available fora value 0 a by d=90 degrees. when 0 was smaller: than- For lighter 90then- 11 was correspondingly smaller. It should be pointed out that theexpressions lag and lead used in connection with c and d are arbitrary.The axis of 9 is referred to as la ging behind that of F because inasynchronous operation the former tries to catch up with the latter.Similarly, f is said to lead the brush axis 26, 24 because d isarbitrarily measured from the time when 1' coincides with the brush axisand because in asynchronous operation f revolves counterclockwise.

If it were possible to make the brush voltage a maximum when theeriodical 'space relation of 9 is that shown 1n Fig. 13, then for 0:90degrees the brush voltage would be less than the maximum, would increaseto a maximum for the value of 0 shown in Fi 13, and then again decrease,thus complete y changing the manner or rate of variation of the brushvoltage with varying c. Genera-lly speaking, 0 decreases with decreasingload. Other things being equal, the value of c for maximum torquedepends on the magnitude of the unidirectional excitation increasingwith increasing excitation. Therefore by causing the maximum brushvoltage to occur for different values of c or even outside the range ofa, it is possible to considerably vary the compounding efiect of theinherent regulating property of such motors.

The maximum brush voltage can be made to coincide with any selectedvalue of c or be displaced by any desired amount from mum when a has thevalue shown in Fig. 13 i and which is smaller than 90.

Instead of displacing the brushes as explained, the phases of thevoltages lmpressed on the slip-rings of 19 may be changed so as to causethe flux f to occupy a different space position with reference to thebrush axis. To cause the brush voltage to be a maximum for the positionof 7 and of 24 and 26 shown in Fi 13, the flux f should be moved (90d)egrees against the direction of rotation of 19, for instance. by meansof the phase regulator 37, 38 of Fig. 1.

Another, and practically very interesting, method of correlating themaximum brush voltage to a selected value of the per odical spacerelation 0 is to displace the axis of 9 or, more generally speaking, theaxispf'the resultant unidirectional rotor magnetization F with relationto the laminations of the rotor 7. The laminations 7 are keyed to thesame shaft as the laminations carrying the exciter winding 19. Ifwithout changing this mechanical connection the winding 9 were sodisplaced or a new winding 9 were so located as to produce amagnetization, say, (90-01) degrees in advance, 1. e. in the directionof rotation, of that produced when 9 was in use and on which thesynchronizing torque setting was based, then the axis of 9 would occupythe position occupied by 9 in Fig. 13 when that or 9 was still 90degrees behind F. Since 9 is now assumed to be inactive, the axis of Fwould coincide with that of 9, the periodical space relation of 9 wouldbe c as it was for 9, but 7" would now be perpendicular to the brushaxis and the brush voltage a maximum. This is all shown in Fig. 1%. Thismeans that by displacing the axis of the unidirectional magnetization Fon the secondary of the motor with relation to that secondary, therelation of the maximum brush voltage with reference to any selectedvalue of 0 can be changed at will. A displacement of said axis in thedirection of rotation is equivalent to a displacement of the exciterbrush axis inthe same direction and the same angular displacement,reduced to electrical degrees, produces the same quantitative change.

When the secondary member of the motor is provided with displacedwindings such as 9, 10 of Figs. 1 or 2 and 4:9, #19", 49 of Figs. 8 and4, which are available for connection to the exciter brushes, then theaxis of the total or resultant unidirectional magnetization F ofthesecondary of the motor can readily be displaced with respect to saidsecondary by connecting a plurality of such windings in parallel to thesame pair or set of exciter brushes and suitably adjusting theresistances of the windings themselves, their number of turns orexternal resistances connected between said windings and the exciterbrushes. Thus the windings 9 and 10 of Fig. 1 may have the same numberof turns and they may be connected in parallel and to the brushes 2 1-,26 for synchronizing the resistances 53, 54, being so adjusted as to,for instance, cause each to produce an equal number of ampereturns. Theresult ant magnetization F will have an axis lying midway between theaxes of 9 and 10. The synchronizing torque setting is now made withreference to the axis oi the resultant F. If a unidirectional torque isdesired, the setting will be such that the alternating brush voltage isa maximum when the axis of F is perpendicular to that of F. If, when themachine reaches synchronism, the resulting inherent variation ofexcitation is not suitable for the purpose in hand, it may be modifiedto any reasonable extent by simply manipulating the resistances 33 and34. f the leading magnetization is it produced by 10 and the axis of theresultant is to be advanced as indicated in Fig. 14, then the number ofampereturns in 10 is increased relatively to that in 9. When themagnitude or the resultant F, but not its relation to the laminations ofthe secondary, is to be modiiicd, then the ampereturns in 9 and in 10are varied in the same ratio.

The axis of F may also be moved through a definite angle by a simplechange of connections. Thus in Fig. 3 after the motor has run up tonearly synchronous speed and short-circuits the windings 49', 49, 49",the brushes 54, may be connected to 49' and 4.9 after 19 has beendisconnected from 50 and the machine synchronized as heretoforeexplained. It the axis of the unidirectional magnetization on thesecondary of the motor is now to be shifted with respect to the statorlaminations, 49 or 49" is disconnected from 50, with the result thattheaxis of F is moved through 30 degrees if the number of turns in 49,49", 49" are the same and through some other angle if they differ fromeach other.

A compromise may often be desirable for the sake of greater simplicity.hen the periodical space relation 0 at which the maximum brush voltageis desired is, for instance, somewhere near 45 degrees, then changesafter synchronization can be avoided by sacrificing synchronizingefficiency in favor of the compounding feature to a greater or smallerextent according to circumstances. The governing factors are as follows: It the synchronizing torque setting differs by 90 electricaldegrees from that which gives an absolutely unidirectional but pulsatingtorque, then the resulting synchronizing torque will be of double slipfrequency and have equal positive and negative maxima, each equal tohalt the available maximum synchronizing torque, an obviouslyundesirable condition. If the ditference is only 45 degrees, thepositive maxima will last three times as long as the negative and thelatter will be but 18% of the former. The maximum torque in this casewill be but 18% smaller than the maximum available and the synchronizingtorque may still be said to be substantially a pulsating torque or. asubstantially unidirectional torque. The fact is that when the phasedilierence is less than 90 degrees, the synchronizing torque has onecomponent which alternates at double slip frequency and another which isunidirectional and pulsates at slip frequency. As the phase differencedecreases the amplitude of the first component decreases and that of thesecond increases. WVhen the amplitude of the pulsating component equalsor exceeds that of the alternating component, the resultant torquebecomes of practical interest and may be said to be substantiallyunidirectional. As the phase difference diminishes still further. theduration and the amplitude of the positive impulses of the resultantsynchronizing torque both increase while those of the nega- .the excit'tive impulses diminish until phase coincideuce is'reached, when allvestige ofa negative torque disappears. It is therefore seen thatthere'is ample room for a reasonably satisfactory compromise even underquite severe requirements as to regulation as well as synchronizingcapacity.

What istrue of the single-phase synchronizing torque is also true of thepolyphase synchronizing effort, except that even better synchronizingresults are secured and for discrepancies in the setting of the ordernamed, only the constancy of the magnitude of the resultant torque isaffected while its direction does not change at any time.

Having fully described and explained the invention, the preferred formof motor and the preferred methods of operation can be shortly stated.Since separately excited motors will mostly be of large size, thepreferred form is selected with large motors in view.

In the preferred form of motor the primary is of the usual constructionand is located on the stator, the secondary carries a squirrel cage 8 orthe like and at least two displaced windings such as 9 and 10 connectedto three or four slip-rings;

The exciter is driven at a higher speed than the motor, its primaryrevolves and cooperates with a single-phase arrangement of stationarybrushes carried by a secondary provided with exciting means whichproduce a unidirectional magnetization at synchronism and permit of theposition of the axis of said magnetization to be adjusted. Adjustableresistances are'provided between the exciter brushes andthe displacedslip-ring windings on the secondary of the motor and other adjustableresistances are connected to shunt the windings on said secondary.

For heavy starting the winding 8 has a. high resistance so the primarycan be connected to the full line voltage at starting.

For easy starting conditions, the winding.-

8 has a lower resistance and the primary is preferably first connectedto less than the full line voltage.

One method of operating such a combina-- tion is to usethe slip-ringwindings to develop at least part of the induction motor torque atstarting, to inject into the parallel connected slip-ring windings nearsynchronism an auxiliary or exciting voltage of slip frequency of amagnitude independent of sai frequency and of a phase to produce asubstantially 'maximum and unidirectional single-phase synchronizingtorque and thereafter, or at synchronism, to change the phase of thesynchronizing voltage to produce the desired'compounding characteristic,for instance by changing the ratio of the amperetums of the sli -ringwindings connected to vo tags. Another is to use the slip-ring windingsto cure a unidirectional'or a substantiall develop at least part of theinduction motor torque at sta'rting,to inject into one of said windingsnear synchronism an auxiliary or excit-in voltage of slip frequency of amagnitude independent of said frequency and of a phase to produce asubstantially maximum and unidirectional single-phase synchronizingtorque and thereafter to change the phase of the synchronizing voltageto produce the desired compounding characteristic, for instance bydisplacing the exciter brushes.

A third method is to use the slip-ring windings to develop at least partof the induction motor torque at starting and to inject into at leastone slip-ring winding an auxiliary or exciting voltage of slip frequencyof a magnitude independent of said frequency and of a phase to produce asubstantially unidirectional single-phase synchronizing torque andsubstantially the desired compounding characteristic in normaloperation.

,A fourth method applicable'to a motor provided with an exciter having apolyphase arrangement of brushes is to use the slipring windings todevelop at least part of the induction motor torque at starting, toinject into a plurality of said slip-ring windings a polyphase auxiliaryor exciting voltage of slip frequency of a ma nitude independent of saidfrequency and of a phase toproduce a synchronizing torque of nearlyconstant magnitude, and thereafter to reduce the amereturns due to allbut one ofsaid auxiliary or voltages the phase of which is also sochosen as to give the desired compounding characteristic when leftconnected to its slipring winding. Where the ampereturns 'nizingcircuits, in which case I believe that the motor will run at asuper-synchronous speed at some loads.

Any auxiliary, or synchronizing, or brush volta derived from myfrequency converter an conductively impressed on the secondary for thepurpose of synchronizing the motor is always of the slip frequency ofthe I secondary of said motor. Its frequency therefore diminishes withdecreasing motor slip becoming zero when said motor reaches s nchronism.The amplitude of this auxi 'ary voltage is however quite independent ofits frequency and when its phase and magnitude are set, as heredisclosed,-to seunidirectional synchronizing torque of su cient value,its ma itude, if no adjustments are made, is maintained at a nearlyconstant value until the motor looks into synchronism. In this ,itdifiers vitally from the voltage generated by the primary flux in thesecondary winding or windings upon which such an auxiliary voltage isimpressed. It is because the magnitude or amplitude of a eneratedvoltage is not maintained as sync r0- nism is approached that it isunable to synchronize the motor. An important feature of my invention istherefore to maintain the magnitude or amplitude of this auxiliaryvoltage as synchronism is approached, and by maintain I mean topreferably keep it at or above a value sufiicient to synchronize themotor and to certainly preserve it from lapsing or declining toinsignificant values as synchronism is approached. Increasing this.voltage as synchronism is approached of course increases thesynchronizing torque, and vice versa.

In order to secure the best starting performance and take full advanta eof the pulsating and substantially uni irectional single-phase or thesubstantially constant polyphase synchronizing torque, the motor ispreferably designed along the lines now recognized as best for polyphaseinduction motors. This means a stator and rotor construction withoutdefined polar projections, distributed windings on both members and assmall an air-gap as mechanical considerations will permit.

It is not necessary for the exciter to be directly coupled to the motoror to be driven in any other manner at the same speed as the latter. Theexciter may have a different number of poles, and may be run at a speeddiffering from that of the motor, preferably at a higher speed, just soprovision is made for a constant ratio of motor and exciter speeds to bemaintained, a matter which can be achieved in a number of known ways,for instance, by suitably proportioned gearing. Where the motor runssynchronously the exciter should also run synchronously. The exciter mayalso be built without defined polar projections and more or lessdistributed windings.

It is'to be understood that a synchronous motor is a machine capable ofoperating at a constant and synchronous speed under varying loadconditions and which does so operate. The synchronous motors describedin this specification carry unidirectional am-.

pereturns on their secondary and unless the organization of the machineis such as to permit, with chan ing torque demand, (1) of an angulardisp aoement between the axis oi said ampereturns and the axis of theresultantmotor magnetization, or (2) of a change in the magnitude ofsaid ampereturns or (3) of said angular displacement and of said changein magnitude, the motor cannot and does not run at a constant and excitesynchronous speed under varying load conditions.

It is further to be understood that by I synchronism is approached andactually becomes zero at synchronism. It is also known that a polyphaseinduction motor can be so modified as to make it capable of operatingsynchronously under varying load conditions. Any torque which, in apolyphase induction motor adapted .to operate synchronously undervarying load, will bridge the gap-between'the induction motor torque ofthe machine, which becomes zero at synchronism, and its synchronismtorque is referred to asa synchronizing torque. I

A synchronous motor is said to be compounded when the unidirectionalampereturns on the secondary are smaller at light than at heavy loads.This change in the unidirectional ampereturns with changing load affectsthe power factor at which the machine operates. The change can be suchthat the power factor remains practically-- constant throughout thesynchronous load range of the motor, or it can be such that the powerfactor is a leading one at light loads, that this lead diminishes withincreasing load and is converted into a lag near the maximum synchronoustorque of the machine. Either of these compounding characteristics arepopular and right now the last named is probably more in demand.

While the invention is illustrated and spedescribed as applied toseparately synchronous induction motors, it will be understood that inmany of its aspects the invention is applicable to self-excitedmachines; furthermore, certain of the features of this invention areapplicable to synchronous motors generally whether wound for single orpolyphase currents. While theories have been advanced as to operation ofthe machines and methods here described, thishas been done witha view tofacilitating the description and it is to be understood that I do notbind myself to these or any other theories.

cificalliy It will be clear that various changesmay be made in thedetails of this disclosure without departingfremthe spirit of thisinvention, audit; is, therefore,-;to be understood that this inventionis not tobe limited-to the specific details here shown and described. Inthe appended claims I aim to cover all the modi 'cations which arewithin the scope of my invention.

Claims j 1. The method of operating a motor which carries variable loadat synchronous speed, comprising, roducing a primary flux which revolveswit respect to the primar causing the primary flux to generate inuctionmotor-torque producing ampereturns on the secondary, introducininto a' winding on the secondary an auxi iary voltage of same frequencyas the voltage generated in the secondary winding by the primary flux atnearly synchronous speeds and in substantiall lew than quadrature haserelation to the generated volt-age an maintaining the magnitude of theauxiliary voltage until synchronism is reached to produce asubstantially unidirectional synchronizing torque.

2. Themethodof operating a motor which carries variable load atsynchronous speed, com rising, roducing a primary flux which revo veswit respect to the prlma causing the primary flux to generate inuctionmotor-torque producing ampereturns on the secondary, introducinginto a winding on the secondary an auxiliary voltage of same frequencyand of about the same phase as the voltage generated in the secondaryWinding by the primary flux at nearly synchronous speeds, andmaintaining the magnitude of the auxiliary voltage until synchronism isreached to produce a synchronizing torque.

3. The method of operating a motor which carries variable load atsynchronous speed, com rising, roducing a primary flux which revo veswit res ect to the primary, causing the primary ux to generateinductionmotor-torque producing ampereturns on the secondary,introducing into displaced windings on the secondary auxiliary phasedisplaced voltages of the same frequency as the voltages generated insaid windings by the primary flux at nearly synchronous speeds and insubstantially less than quadrature phase relation to the correspondinggenerated voltages, and maintaining the ma ni tude of the auxiliaryvoltages until sync ronism is reached to produce phase displaced andsubstantially uni-directional synchronizing torques.

4. The method of operating a motor which carries variable load atsynchronous speed,

com rising, roducing-aprima flux which revo ves wit respect to theprimar causing the primary ux to generate in uctionmotor-torqueproducing ampereturns on the secondary introducin into a. winding on thesecon ary an auxl 'ary voltage of same 'frequency as the voltage"generated in the secondary winding by the primary flux at unidirectionalnearly synchronous speeds, said auxiliary voltage having an amplitudeindependent of its fre uency and becoming unidirectional at sync ronism,and adjusting the phase of I e interaction of a primary flux which ro-'volveswith respect to the primary and a secondary, comprisingintroducing into dis-i placed windings on the secondary, phase displacedvoltages which near synchronism are of slip frequency and areunidirectional at synchronism, adjusting the phases and magnitudes ofthe voltages to produce near synchronism a substantially constant syncironizing torque, and changing the rela tive adjustments of the twointroduced voltages after synchronism has been reached.

6. The method of operating a motor which carries'variable load atsynchronous speed, comprising, producing a 7 primary flux which revolveswith respect to the primary, causing the'primary flux to generatesecondary torque producing currents in relatively displaced secondarycircuits at speeds below synchronism, producing an auxiliary voltagewhich is of slip frequency at subsynchronous speeds, of an amplitudeindependent of its frequency and unidirectional at synchronism,impressing an auxiliary voltage on two of the displaced secondarycircuits to produce a substantially unidirectional synchronizing torqueand at synchronism the unidirectional magnetization of the motor, andadjusting the axis of the resultant secondary unidirectionalmagnetization with reference to the axis of a secondary circuit. 7

7. A motor which carries variable load atsynchronous speed, having aprimary member adapted to produce a primary flux which revolveswithrespect to the primary, a secondary member having a winding ininductive relation to said primary flux, means for impressing on saidsecondary winding an auxiliary voltage which is of sllp frequency and ofan amplitude independent of its frequency, and means for controllin thephase of said voltage relatively to the p ase of the voltage generatedin said secondary, winding by the primary flux adapted to produce nearsynchronism a substantially unidirectional synchronizing torque. q

8. A motor which carries variable load at synchronous speed, ada tedproduce a primary flux which revo ves with res ect to the rirnary, asecondar member av1ng dis aced windings in in uctive relation to saiprimary flux, means for'impressing on said secondary winding phasedisplaced auxiliary voltages which are of slip fre quency and of anamplitude independent of their frequency, and means for controlling thephases of the auxiliary voltages with respect to the phases of thevoltages generated in the displaced windings on thesecondary by theprimary flux adapted to produce near synchronism a plurality of phasedisplaced and substantially unidirectional synchronizing torques and atsynchronism a unidirectional magnetization the torque producingcomponent of which varies with varying motor load. i

9. A motor which carries variable load at synchronous speed, having aprimary member adapted to produce a primary flux which revolves withrespect to the primary. a secondary member having a windin in inductiverelation to said primary ux, means for impressing on said secondarywinding an auxiliary voltage which is of slip frequency, of an amplitudeindependent of its frequency and which is unidirectional at synchronism,and means for controlling the phase of said auxiliary voltage withrespect to the phase of the voltage generated in the winding on thesecondary by the primary flux adapted toproduce near synchronism asubstantially unidirectional synchronizing torque and adapted to produceat synchronism a unidirectional magnetization which increases with theload.

10. A motor which carries variable load at synchronous speed,comprising, a primary member havin a winding adapted for connection toan aternatin current supply, a secondary member a apted to produce aunidirectional magnetization, an exciter supplying to the secondary atsynchronism a unidirectional voltage which changes in magnitude withchanging synchronous motor load, and means for varyingthe axis of theunidirectional magnetization produced by the secondary member withrespect to that member for the purpose of changing the relation betweenchangingmotor load and changing secondary magnetizatron.

11. A motor which carries variable load at synchronous speed,comprising, a primary member having a winding adapted for connection toan alternating current supply, a secondary member having two displacedwindings, an exciter driven to revolve synchronously when the motor sorevolves, means including the primary of the exciter for producing inthe exciter a flux which revolves with the line frequency with respectto the primary of the exciter, brushes on the exciter adapted to beconnectedto both of the windings on the secondary and means for varyingthe relation of the. ampere turns produced by the two windings.

12. A motor which carries variable load at synchronous speed, com risina primary member having a win inga apted for connection to analternating current supply, a secondary having a winding, an exciterdriven to revolve synchronously when the motor so revolves, meansincluding the primary of the exciter for producing in the exciter a fluxrevolving with line frequency with respect to the exciter primary,brushes on the exciter adapted to be connected to the secondary winding,and means for producing in the exciter another magnetization which isunidirectional and always stationary with respect to said brushes.

13. A motor which carries variable load at synchronous speed, comrising, a rimary member havin a win ing adapte to produce a primary uxwhich revolves with respect to the primary, a secondary member having awinding, means for producing and impressing on the secondary windin asynchronizing voltage of a magnitu e independent of its frequency and ofsame frequency as that of the voltage generated in said winding by theprimary flux, and means for controlling the base of the synchronizingvoltage adapted, at speeds very near the synchronous, to cause it topass through zero approximately when the axis of the secondary windingcoincides with the axis of the primary flux.

14. A motor which carries variable load at synchronous speed, having aprimary member adapted to produce a primary flux which revolves withrespect to the primary, a secondary member having a winding in inductiverelation to the primary flux, a source of auxiliary volta e, and meansincluding the windin on t e seconda and said source adapte to produce asu stantially unidirectional and pulsating synchronizing torque betweenprimary and secondary members, whereby the motor can. be brought intosynchronism and caused to o erate synchronously at a plurality of 108.s.

15. A motor which carries variable load at synchronous speed, having aprimary member adapted to produce a primary flux which revolves withrespect to the primary, a secondary member having a winding in inductiverelation to the primary flux, a source of auxiliary voltage, and meansincluding the winding on the secondary and the said source adapted toproduce between the primary and secondary members an alternatingsynchronizing torque the positive maxima of which substantially exceedits negative maxima, whereby the motor can be brought into synchronismand caused to operate synchronously at a plurality of motor loads.

16. A motor which carries variable load at s nchronous speed, having aprimary mem 1' adapted to produce a primary flux which revolveswithrespect to the primary.

a secondary member ca ing displaced generate hase dis laced s n windin sin inductive relat on to the pritorques which combin to forni if maryux, a source of auxiliary volt-ages, continuous torque of varyingmagnitude be- 10 5 means including the displaced windings on tween theprimary and secondary members. the secondary and the source adapted topro- In testimony whereof I aifix my signature duce auxiliaryampereturns on the secondthis 2nd day of February 1924. v arycooperating with the primary flux to VALERE AL FRED FYNN Certificate ofCorrection.

It is hereb certified that in Letters Patent No. 1,599,7 56, grantedSeptember 14, 1926, upon t e application of Valere Alfred Fynn, of St.Louis, Missouri, for an improvement in Synchronous'Motors, errors appearin the printed specification retiring correction as follows: Page 5,line 113', for the word other read at 8; page 7, line 47, for the wordinstance read instamf-page 11, line 110, for the word excited readwaiter, page 13, line 101, claim 6, for the word an read the; and thatthe'said Letters Patent should be read with these corrections thereinthat the same may conform to the record of the casein the Patent Oflice.

- Signed and sealed this 26th day of October, A. D. 1926.

[emu] WM. A. KINNAN, Acting Commissioner of Patents.

